Supreme Commander on HD4850?

I'm planning on buying a new HD4850 and I was wondering if I will be able to manage good frame rates with max details.
I will be running at 1280x1024 and I don't care really all that much about AA/AF as long as the options are high and fps is smooth enough.
Also, I constantly use the space bar to change the view angle to look at units in various angles. Will that drop the fps a LOT?
I believe SC is smoothly playable now, because from what I have seen from Youtube videos the motion is very smooth.
Or maybe should I spend a lil bit more and get the HD4870... is it worth the extra cost? (the cheaper the better for me, I'm on budget)

Help would be much appreciated, thanks.

Yeah, SupCom relies much more heavily on the CPU than the GPU. What CPU do you have? If I remember correctly during benchmarks around its launch, it was nearly impossible to get smooth framerates with 7 CPU-controlled players without a quad-core.